1. Field of the Invention
The present invention relates to a steering system for vehicles, and particularly, to a steering system for vehicles of the type in which a rear wheel is steerable in relation to the steering operation of a front wheel.
2. Description of Relevant Art
The present applicant has already proposed a steering system for vehicles in which a rear wheel is steerable in relation to the steering of a front wheel, such that the steered angle ratio of the rear wheel to the front wheel is variable in accordance with the vehicle speed. (Japanese Laid Open Application No. JP-A-59-26363 dated Feb. 10, 1984).
More particularly, in this steering system, the rear wheel is steered, at relatively low vehicle speeds, in the opposite direction to the front wheel or substantially at an angle of zero degree and, at relatively high vehicle speeds, in the same direction as the front wheel. The steered angle ratio is given as a continuous function of the vehicle speed, as represented by a curve X of FIG. 6, such that for vehicle speeds higher relative to a predetermined vehicle speed d.sub.2 the angle ratio is positive, that is, the steered angles of the front and rear wheels are the same in phase, and for vehicle speeds lower relative thereto the angle ratio is negative, that is, the steered angles are opposite in phase. Thus, a continuous control of the steered angle ratio is achieved to be effected along the function curve X, ranging from a low speed to a high speed. As a result, at relatively low vehicle speeds, the minimum turning radius of the vehicle as well as the inside wheel span is remarkably reduced, and in addition the vehicle turning characteristic such as when parking, travelling along a narrow curved road, or making a U-turn, is favorably facilitated. Moreover, at relatively high vehicle speeds, the steering responsiveness can be highly improved.
Incidentally, in such steering system, the control of the steered angle ratio is effected to be continuously variable by means such as of an electric motor controlled with a computer mounted on the vehicle, so that the motor or the like is put in service each time the vehicle speed changes even in the case of a slight change, thus resulting in a relatively larger power consumption. Moreover, such frequent service may result in deterioration in the endurance of a rear wheel steering mechanism which is generally designed sound enough to endure relatively large stresses imposed thereon in its motion corresponding to the variation of the steered angle ratio.
With such points in mind, the present invention has been achieved to provide an improvement in a steering system for vehicles of the above-mentioned type.